gcp: Allow GCB service agent for kubernetes-release-test

Ref:
  - kubernetes/release#3729

Temporary allow the Service Agent for the GCB Service from project
`kubernetes-release-test`. This will enable artifacts release for
Kubernetes to a community-owned bucket.

infra/gcp/terraform/k8s-infra-releases-prod/main.tf

@@ -49,6 +49,14 @@ resource "google_storage_hmac_key" "fastly_reader_key" {
   service_account_email = google_service_account.fastly_reader.email
 }
 
+// TODO: remove this after https://github.com/kubernetes/release/issues/3425
+resource "google_storage_bucket_iam_member" "release_object_admin" {
+  bucket     = module.k8s_releases_prod.bucket_name
+  role       = "roles/storage.objectAdmin"
+  member     = "serviceAccount:[email protected]"
+  depends_on = [module.k8s_releases_prod]
+}
+
 resource "google_storage_bucket_iam_member" "fastly_reader" {
   bucket     = module.k8s_releases_prod.bucket_name
   role       = "roles/storage.objectViewer"